1. Field of the Invention
The present invention relates to the removal of deposits from contact lenses, particularly soft contact lenses. More specifically, the present invention relates to aqueous contact lens cleaning compositions and to methods for removing protein, lipid, and calcium deposits from contact lenses using these compositions.
2. Description of the Prior Art
The compositions and methods of the present invention are especially useful in removing deposits from soft contact lenses. The "soft" lenses referred to herein are generally those lenses formed from a soft and flexible material. Although the present invention is not directed toward the manufacture of soft contact lenses, it should be noted as general background for this invention that various materials and methods for producing soft contact lenses have been described in the art. For example, U.S. Pat. Nos. 3,503,393 and 2,976,576 describe the use of various polymeric hydrogels based on acrylic esters in the manufacture of soft contact lenses. It is also known in the art that soft contact lenses may be based on silicone and other optically suitable flexible polymers. The general physical characteristics of soft contact lenses are due at least in part to the fact that these lenses absorb a high percentage of water. Due to this hydration, the polymer swells to form a soft and flexible material, thereby resulting in a physically stable material capable of maintaining its shape and dimensions.
One of the major problems associated with the use of soft contact lenses is the formation of deposits when these lenses are worn on the human eye. The composition of these deposits is complicated and varies from patient to patient; however, the deposits are believed to primarily consist of proteins, lipids and calcium. The deposits may form both on the lens surface and beneath the lens surface. The buildup of material on and below the surface of the lens creates discomfort and irritation in the eye of the patient.
The material attached at the lens surface can be removed by mechanically rubbing the lens with cleaning solutions containing microspheres and other chemical agents. However, repeated cleaning of the lens in this manner may result in physical damage to the lens surface, which damage can be identified microscopically as scratches, depending on the nature of the microspheres or beads utilized in the solutions, for example. Moreover, it is generally either difficult or impossible to remove deposits located beneath the lens surface using prior art cleaning solutions and mechanical rubbing of the lens.
The deposits attached to the lens surface consisting of proteinaceous material can be removed by enzymes; see in this regard U.S. Pat. Nos. 3,910,296 and 4,096,870. Also, molecular mechanisms for removing cross-linked (denatured) proteins from surfaces with chemical cleaners are described in detail in U.S. Pat. No. 4,311,618. However, nonproteinaceous and proteinaceous materials beneath the lens surface are generally more difficult to remove with enzyme or chemical cleaners.